1. Field of the Invention
The present invention relates to a camera shake alarming apparatus suitable for use with, e.g., a camera.
2. Related Background Art
When taking a photo by a conventional camera held with hands, and if, for instance, a lens having a large focal length is employed, or if a shutter speed is decreased, an image blur of the photo is produced by an influence of a camera shake. This may result in a degradation of picture quality thereof in some cases.
Under such circumstances, the cameras offered of recent years have been constructed so that the camera shake can be compensated by moving some parts or the entire optical system (lens groups) in a direction orthogonal to the optical axis to cancel the camera shake.
The camera described above have also been constructed to give an alarm indicating that the picture quality of the photo will be degraded due to the camera shake if the camera shake can not be (entirely) compensated because of a large amount of camera shake even by moving the optical system to, as explained earlier, cancel the camera shake.
Another type of camera is known in which there is no provision for shake compensation, but if the amount of camera shake is large enough to degrade the picture quality of the photo, an alarm therefor is given.
That is, as disclosed in, e.g., Japanese Patent Application Laid-open No. 2-126249, a limit shutter speed as a shutter speed at which excessive camera shake begins to occur is calculated based on the focal length of the lens. This limit shutter speed is compared with a shutter speed set in the camera when taking the photo. Then, the alarm for the camera shake is given according to this comparison result.
Incidentally, if a magnification during the photography is large in this type of camera, the camera is regarded to be fixed to, e.g., a tripod or the like, and the arrangement is such that no alarm for the camera shake may be given.
The limit shutter speed is, as explained above, determined based on the focal length of the lens. The limit shutter speed therefore becomes a fixed value depending on the lens irrespective of the magnification when performing the photography. However, even if the amount of camera shake is the same on the camera side, an image blur of the photo increases in proportion to an image magnification.
Hence, when taking the photo by decreasing the image magnification, there arises a problem in which the alarm for the camera shake is unnecessarily given depending on the shutter speed set in the camera regardless of the fact that there is almost no image blur of the photo due to the camera shake.
Further, if the optical system of the camera is of a so-called inner focus optical system, the focal length of the lens constituting the optical system thereof varies depending on a subject distance. Nevertheless, the limit shutter speed described above is calculated, with the focal length regarded as a fixed value.
For this reason, an error is produced in the limit shutter speed. The alarm for the camera shake is still unnecessarily given. Further, the alarm for the camera shake may be required, but not given in some cases.